#define   _CRT_SECURE_NO_WARNINGS 1
//*
// * Definition for singly-linked list.
// * struct ListNode {
// *     int val;
// *     struct ListNode *next;
// * };
 
typedef struct ListNode ListNode;
bool hasCycle(struct ListNode* head) {
    ListNode* slow = head;
    ListNode* fast = head;
    while (fast && fast->next)
    {
        slow = slow->next;
        fast = fast->next->next;
        if (fast == slow)
        {
            return true;
        }
    }
    return false;
}